Methods and apparatus for heating a body conveyor system for heating bodies by a microwave cavity

ABSTRACT

Method and apparatus for heating a body, especially a long continuous body such as rubber belting, by microwave heating in an enclosure which is moved relative to the body being heated. In the examples described this is done by a reciprocating device, the belting being held stationary during heating. The support structure on which the enclosure is movably mounted is preferably pivoted at one end on a fixed axis and pivoted at the other end to the moving platen of a vulcanization press.

Inventor Peter Astley Wincott Luton, England Appl. No. 782,389 FiledDec. 9,1968 Patented June 1, 1971 Assignee The Eglish Electric CompanyLimited London, England Priority Dec. 9, 1967 Great Britain 56105/67METHODS AND APPARATUS FOR HEATING A BODY CONVEYOR SYSTEM FOR HEATINGBODIES BY A MICROWAVE CAVITY {56] References Cited UNITED STATES PATENTS3,277,580 10/1966 Tooby 219/10.55 2,603,741 7/1952 Seifried et a1.219/10.55X 2,722,589 11/1955 Marguardt.... 219/10.61 3,177,333 4/1965Lamb 219/10.55 3,436,506 4/1969 Smith 2 l 9/1055 FOREIGN PATENTS 944,993 12/1963 Great Britain 219/ 10.55

Primary ExaminerJ.V. ruhe Asristan! Examiner-LB. BenderAttorneysMisegades & Douglas, Keith Misegades and George R. Douglas Jr.

ABSTRACT: Method and apparatus for heating a body, especially a longcontinuous body such as rubber belting, by

2 Claims 3 Drawing Figs microwave heating in an enclosure which is movedrelative to US. Cl 20/101159, the body being heated. 1n the examplesdescribed this is done 219/1055, 219/ 1() 7 3 by a reciprocating device,the belting being held stationary Int. Cl H05b 5/00, during heating. Thesupport structure on which the enclosure H05b 9/06 is movably mounted ispreferably pivoted at one end on a fixed Field of Search 219/ 10.73,axis and pivoted at the other end to the moving platen of a vul- 10.55,10.61 canization press.

MICROWAVE SOURCE 2o\fl MUmDOw ATENTED JUN 1 m1 SHEET 2 OF 3 PATENTED JUNHan SHEET 3 0F 3 FIG.3

METHODS AND APPARATUS FOR HEATING A BODY CONVEYOR SYSTEM FOR HEATINGBODIES BY A MICROWAVE CAVITY This invention relates to methods andapparatus for heating a body by microwave energy and to bodies soheated.

Microwave energy, that is to say the energy in radio frequencyradiation, has for some time been known to induce heating in materialswhich are not transparent or reflective to such radiation. It is usualto provide a microwave enclosure, (sometimes called a microwave cavityor microwave oven) which consists essentially of an enclosed chamberhaving an inlet for the radiation. The body to be heated is placed inthe enclosure and subjected to the radiation which is supplied throughthe inlet from a suitable source such as a magnetron. Perhaps the bestknown example of an application of this method up tonow is in thecooking of food: microwave cooking ovens are available commercially.

Microwave heating has the advantages over more conventional heatingmethods which involve heating the atmosphere around the body to beheated (so that heat is transferred to the body from said atmosphere),that:

a. the atmosphere is not itself heated by the microwaves,

and

b. the enclosure can be arranged so that virtually the only substancesexposed to the radiation, which are not transparent and reflectivethereto, are those of the body to be heated. Thus substantially all ofthe energy produced can be converted into heat in the body, so thatthere can be negligible waste heat. This, combined with the fact thatradiation of considerable-intensity can be produced quite easily, meansthat the body can be heated very much more quickly than by moreconventional methods, and also in most cases more economically.

One problem inherent in microwave heating is that, because the heat isproduced within the body being heated by virtue of radiation directed atthe body in a straight beam or beams (direct from the microwave sourceand/or by reflection from suitable surfaces), standing patterns ofradiation are set up which make it difficult to obtain a substantiallyeven temperature distribution over the surface of the body. ln practice,hot spots," i.e. points at which the temperature is considerably higherthan in the surrounding parts of the surface, tend to occur on thesurface of the body by virtue of these standing patterns.

An object of the present invention is to reduce the effect of hot spotsand thus tend to promote a more even temperature distribution on thesurface of the body to be heated than has hitherto been possible inmicrowave heating techniques.

The body to be heated may be (for example) a single separate article oran elongate body such as a sheet or strip. lt has been proposed to heatsheet or strip material in a microwave enclosure in which the materialto be heated is held stationary or is passed through the enclosure witha steady unidirectional movement. In the latter case, the continuousmovement of the material through the enclosure will tend to eliminatethe effect of hot spots; but such continuous movement is not alwayspossible or desirable for various reasons. For example, if the heatingprocess is part of a process of which the next stage requires that partof the sheet or strip shall be stationary, then the whole sheet or stripmust be stationary.

It is therefore a further object of the invention to provide a means ofreducing the effect of hot spots where the body to be heated isstationary while being heated by microwave energy.

The term sheet material" as used herein includes materials in the formof discrete sheets and elongate sheets or strips for example conveyorand transmission belting, including V-belting, and is limited tomaterials having dielectric properties suitable for allowing heating ofthe material by absorption of microwave energy, for example natural andsynthetic rubbers and plastics materials. A body heated or to be heatedby methods and in apparatus according to the present invention maycomprise sheet materials as defined above.

The term microwave enerby" as used herein means electromagnetic energywithin the approximate frequency range 300 to 30,000 megacycles/second.

The usual method of reducing the effect of hot spots is to employ adevice known as a mode stirrer, which is a rotatable bladed device inwhich the blades are inclined in opposite directions to each other so asnot to act as a fan but to stir the microwave beam. This does noteliminate the hot spots however; it merely reduces the temperature ofeach hot spot. The provision of at least one mode stirrer in associationwith the source of microwave energy (or with each said source if thereis more than one) is to be assumed in interpreting the claims and theremainder of this specification, since the use of mode stirrers isessential in practice.

According to the invention in one aspect, in a method of heating a bodyby microwave energy, the body is heated in a microwave enclosure by amicrowave source which is subjected to movement relative to the bodywhile heating the body, the body being stationary.

According to the invention in another aspect, in a method of heating abody by microwave energy, the body is heated in a microwave enclosurehaving means for admitting said energy into the enclosure from amicrowave source wherein the body is stationary and the enclosure issubjected to movement relative to the body while heating the body, thebody being stationary.

According to the invention in another aspect, in a method of heating abody by microwave energy, the body is heated in a microwave enclosurehaving means for admitting said energy into-the enclosure from'amicrowave source wherein the body is stationary and the enclosure issubjected to movement relative to the body while the body is beingheated.

Preferably, said movement is reciprocating movement. The movement of theenclosure relative to tlgestationary body ensures that the hot spots donot remain stationary for more than an instant, if at all.

Where said body is a continuous elongate body longer than the enclosure,successive portions of the body are preferably moved into the enclosure,stopped, heated and then moved out of the enclosure.

According to the invention in a further aspect, a method of preparingrubber sheet material for vulcanization in a press includes introducinga portion of the sheet material into a microwave enclosure; heating saidportion in the enclosure by microwave energy while the sheet material isstationary and while the enclosure is subjected to reciprocating motionrelative to the sheet material; moving the sheet material so that theheated portion thereof enters a vulcanizing press adjacent the enclosureand so that the next adjacent portion of the sheet material is then inthe enclosure; and pressing the heated portion in the press.

According to the invention in yet another aspect, apparatus for heatinga body by microwave energy includes a microwave enclosure having meansfor admitting microwave energy to the body, support means for holdingthe body stationary independently of the enclosure, and means for movingthe enclosure relative to the body.

According to a preferred feature of the invention, where the enclosurehas an inlet opening for admission of the body, said inlet opening isprovided with a choke for reducing escape of microwave energy from theenclosure.

According to another preferred feature of the invention, the enclosurehas said inlet openingat one end and an exit opening at the other end,said exit opening also being provided with a said choke.

Said support means preferably includes a conveyor belt mountedindependently of the enclosure but passing therethrough through saidopenings.

The apparatus preferably includes a bed fixed in the enclosure so as tosupport the conveyor belt.

Where the means for moving the enclosure is a reciprocating device forapplying motion to the enclosure, the reciprocating device and supportmeans are preferably mounted on a support structure on which theenclosure is mounted for linear motion relative to the support structurein response to said reciprocating motion. ln such an apparatus, the saidsupport structure is pivoted adjacent one end of the enclosure on afixed axis and is pivoted adjacent the other end of the enclosure to afirst part of a press which is movable relative to a cooperating secondpart of the press for pressing a portion of an elongate body previouslyheated in the enclosure.

In one preferred form of apparatus according to the invention, theenclosure includes a plurality of intercommunicating cells each having asource of microwave energy and mode stirring means.

A body heated by a method, and/or in apparatus, according to thisinvention, is included in the scope of the invention.

Heating apparatus in two forms according to the invention will now bedescribed, by way of example and with reference to the accompanyingdiagrammatic drawings, ofwhich:

FlG. 1 is a diagrammatic part sectional elevation showing a microwaveenclosure in one form, in combination with a steam-heated flat moldingpress;

FIG. 2 is a part sectional elevation showing a microwave en closure inanother form; and

FIG. 3 is a cut away general view of a typical choke for a microwaveenclosure.

With reference to FIG. 1, a rectangular microwave enclosure (or cavity)1 has two inputs 2 connected to a source of microwave energy 3 thefrequency of which is 2,450 megacycles/second. Each input 2 isassociated with one of two mode stirrers 4, located within the enclosure1 and each driven by an electric motor 5.

The enclosure 1 is supported by flanged wheels 6 which engage and arearranged to run along rails 7. A reciprocating unit 8, incorporating anelectric motor and crank, is con nected to the enclosure 1 by aconnecting rod 9 and pivot 10 for reciprocating the enclosure 1 alongthe rails 7. The frequency and stroke of the reciprocating motion of theunit 8 are respectively about 6 cycles/minute and about l5 cm.

The opposite ends 11 of the enclosure 1 have horizontal slots 12arranged for the passage of rubber conveyor belting (Which is to beheated in the enclosure) into, through and out of the enclosure 1.

The slots 12 are defined by chokes 13 arranged to prevent emission ofmicrowave energy from the enclosure 1 through the slots 12.

In the arrangement shown in FIG. 1, the enclosure 1, rails 7 andreciprocating unit 8 are supported on vertical hydraulic rams 14. Therams 14 are capable of moving the enclosure 1, rails 7 and unit 8vertically.

Closely adjacent the end of the enclosure 1, remote from the unit 8, isa flat molding press 15. The press 15 has a fixed body 16 and a movableplaten 17. The body 16 has a fixed platen 18. The movable platen l7 andthe fixed platen 18 having cooperating metal surfaces, heated by steam,between which rubber conveyor belting to be consolidated can be placedfor molding,

The movable platen 17 is supported by three hydraulic rams 19. The rains19 are capable of moving the movable platen vertically, and, incooperation with the fixed platen 18, of subjecting rubber conveyorbelting placed between the platens 17 and 18 to a pressure of at least175,000 kg./m. (250 pounds per square inch).

The platens 17 and 18 are heated by steam introduced to the press 15 byway of an inlet 20 and exhausted from the press 15 by way of an outlet21. The slots 12 and platens 17 and 18 are aligned so that rubberconveyor belting can pass straight through the enclosure 1 and betweenthe platens l7 and 18.

Adjacent the end of the enclosure 1 remote from the press 15 is ahydraulically actuated gripper shown diagrammatically at 22, which whenoperated grips the rubber conveyor belting. Adjacent the end of thepress 15 furthest from the enclosure 1, and attached to the movableplaten 17, is a hydraulically operated stretcher shown diagrammaticallyat 23, which, when operated after the gripper 22 has gripped the rubberconveyor belting, grips and stretches the rubber conveyor beltingsuspended between the gripper 22 and the stretcher 23 by a predeterminedamount. The gripper 22 and stretcher 23 are arranged to grip the rubberconveyor belting at a position in which the belting suspendedtherebetween passes straight through the slots 12 and between theplatens l7 and 18.

The rams 14 and 19 are supplied with hydraulic fluid by way of a pipe 24from a source'not shown. All rams 14 and 19 are arranged to operate insynchronism with each other.

In an example of operation of the apparatus according to FIG. 2, asection of rubber conveyor belting 24, comprising severalrubber-impregnated canvas plies bonded between rubber outer covers, isto be vulcanized in the press 15. The section of belting 24 ispositioned in the enclosure 1, and the gripper 22 and stretcher 23 areoperated to engage and stretch the belting. The enclosure 1 is suppliedwith microwave energy from the source 3, the mode stirrers 4 being atthe same time rotated by the electric motors 5, and the reciprocatingunit 8 being operated to reciprocate the enclosure 1 inch relative tothe conveyor belting.

The said section of belting is heated by the microwave energy in theenclosure to a temperature of between C. and C. When the requiredtemperature is reached, the gripper 22 and stretcher 23 are released.The rubber conveyor belting is then moved through the apparatus (bymeans not shown) until the heated section of belting is between theplatens 17 and 18 of the press 15. The gripper 22 and stretcher 23 arethen operated again to engage and stretch the belting. The rams 14 and19 are now supplied with hydraulic fluid so as to raise the movableplaten 17, the enclosure 1, reciprocating unit 8, gripper 22 andstretcher 23 until the heated section of belting 24 is clamped firmlybetween the platens l7 and 18. During this operation the belting stillextends in a straight line through the apparatus. The platens l7 and 18,supplied with steam by way of the inlet 20, raise the temperature of theheated belting still further to the vulcanizing temperature of betweenC. and C, and exert a pressure in the approximate range 175,000-315,000kg./m. (250-450 pounds/square inch) on it.

The combination of this temperature and pressure vulcanizes the rubberconveyor belting.

The apparatus can accommodate a range of different thicknesses andwidths of rubber conveyor belting and the time taken to heat these tobetween 80 C. and 100 C. can be maintained substantially constant byadjustment of the power supplied by the source 3.

It will be appreciated that a section of rubber conveyor belting isheated in the enclosure 1 at the same time as a section already heatedin the enclosure 1 is vulcanized in the press 15.

It will also be appreciated that the length of the section accommodatedin the enclosure 1 is the same as that of the section vulcanized by thepress 15.

The enclosure 1 is also suitable for use in combination with acontinuous press. in this case belting is passed continuously throughthe enclosure 1 and the continuous press.

It will be appreciated that means may be provided for supporting sheetmaterial in and/or for conveying sheet material through the enclosure.

It has been found that belting, having discrete metal inserts extendinglaterally of the belting, can be heated in apparatus and by methodsaccording to the invention.

The apparatus shown in FlG. 2 is similar in principle but constructeddifferently from that in FIG. 1. in H0. 2, the jacks 14 are omitted andthe microwave unit, comprising a microwave enclosure, shown at 30, issupported on a rigid support frame 31 which is mounted through a pivot32 at one end to a fixed pedestal 33, and through a pivot 34 at theother end to a part of the press 15 which carries the lower platen 17and which is movable up and down relative to the upper platen 18 bymeans of the jacks l9.

The microwave unit is arranged as follows. The enclosure 30 consists ofa number of open-ended rectangular cells 35 (two of which are shown insection), mounted in a framework 36 comprising longitudinal l-beams 37which carry upstanding portal frames 38 between which the cells 35 aresupported. The framework 36 is mounted for limited longitudinal movementon the support frame 31 by means of rollers 39 carried by the beams 37.The rollers 39 can roll in guides 40 fixed to the support frame 31. Amotor 41, mounted in the support frame 3], drives an oscillatingmechanism 42 which is coupled to the framework 36 so as to oscillate theenclosure 30 backwards and forwards.

Chokes 43 are provided at each end of the enclosure 30, to preventescape of microwave energy from the latter through the holes in the endsthereof through which the rubber belting 24 to be heated passes. Thebelting 24 is carried through the enclosure 30 by a continuous conveyorbelt 44, of polypropylene or other material substantially transparent tomicrowave energy. The belt 44 extends through the enclosure 30 andpasses over rollers 45 to 49 mounted on the support frame 31. Theroller, 45 is motor driven so that the conveyor belt 44 and rubber belt24 are moved through the enclosure in the direction indicated in theFigure.

A bed, shown diagrammatically at 50, extends longitudinally through theentire length of the enclosure 30. The bed 50, which is of heavypolypropylene or other material substantially transparent to microwaveenergy, is rigidly supported in the enclosure 30 so as to preventsagging of the belt 44.

Each cell 35 has its own microwave source, shown diagrammatically at 51,at the top, and a mode stirrer 52 associated therewith.

In operation, the roller 45 is driven so as to bring into the enclosure30 a section of the belt 24 equal in length to the enclosure. The roller45 is then stopped. The motor 41 is started, and at the same time themicrowave sources 51 and mode stirrers 52 are energized. The belt 24 isthus subjected to microwave energy which heats it to the requiredtemperature. The incidence of hot spots is reduced by the mode stirrers,the hot spots being moved continuously back and forth along the belt bythe oscillating action of the unit 42.

It should be noted that since microwave heating effects tend to bereduced close to metal surfaces, the bed 50 should be supported in sucha way as to support the conveyor belt 44 and belt 24 as far as possibleaway from any metal below it.

For this purpose the bed may itself be supported in the enclosure 30 bya support structure made entirely or partly of a material transparent tomicrowave energy. In this connection it will be appreciated that the bedpreferably oscillates with the enclosure, as it does in the exampledescribed.

The chokes to be used at the open ends of microwave enclosures inapparatus according to the invention can be of any suitable design forpreventing harmful microwave energy from escaping. Their precise designis dependent on the dimensions and character of the material to beprocessed by the apparatus. Such a choke typically comprises severalhollow microwave elements, i.e. spaces, which may be interconnected, thedimensions of these elements being such as to align and alternate themicrowave power in such a way that any radiation from the open outer endof the choke is below the permitted maximum power level.

One example ofa choke of this kind is shown in FIG. 3, and consists of asingle hollow fabricated aluminum member 60, having a rectangularopening 61 at the outer end and another, 62, at the other end, at whichthe choke is fixed to the outside of the end wall 63 of a microwaveenclosure. The member 60 has three pairs of transverse channel sectionenlarged portions 64-66, each constituting a microwave element such thatthe enlarged portions serve to align and alternate, as discussed above,microwave power escaping through the opening 62.

It will be realized, however, that the microwave elements of the chokeneed not be transverse or of channel section.

lclaim: 1. Apparatus for heating an elongate body by microwave energy,including a microwave enclosure having means for admitting microwaveenergy to the body, support means for holding the body stationaryindependently of the enclosure, and a reciprocating device forsubjecting the enclosure to a reciprocating motion in a directionparallel to the plane of the body, said enclosure having an inletopening at one end for admission of the body and an exit opening at theother end, a choke being provided at each of said inlet and exitopenings for reducing escape of microwave energy from the enclosure, andsaid support means including a conveyor belt mounted independently ofthe enclosure but passing therethrough through said openings.

2. Apparatus according to claim 1, including a bed fixed in theenclosure so as to support the conveyor belt.

1. Apparatus for heating an elongate body by microwave energy, includinga microwave enclosure having means for admitting microwave energy to thebody, support means for holding the body stationary independently of theenclosure, and a reciprocating device for subjecting the enclosure to areciprocating motion in a direction parallel to the plane of the body,said enclosure having an inlet opening at one end for admission of thebody and an exit opening at the other end, a choke being provided ateach of said inlet and exit openings for reducing escape of microwaveenergy from the enclosure, and said support means including a conveyorbelt mounted independently of the enclosure but passing therethroughthrough said openings.
 2. Apparatus according to claim 1, including abed fixed in the enclosure so as to support the conveyor belt.